1. Field of the Invention
The present invention relates to an image forming apparatus and a sheet supply apparatus having a plurality of sheet supply units.
2. Description of the Related Art
Conventionally, an image forming apparatus such as a copier, a printer, or a facsimile machine has a sheet storage unit (sheet feeding cassettes) in which recording sheets are stored, feeds a recording sheet from the sheet storage unit using a sheet feeding unit, and conveys the recording sheet to an image forming unit. The image forming apparatus then forms an image on the recording sheet, and discharges the recording sheet from the image forming apparatus.
As an example of the sheet feeding apparatus, an air sheet feeding apparatus adopting an air separation method has been proposed (see Japanese Laid-Open Patent Publication (Kokai) No. 2005-162419). This air sheet feeding apparatus is comprised of a sheet stacking unit on which sheets are stacked, a sheet loosening unit that loosens upper sheets by blowing air to ends of the sheets stacked on the sheet stacking unit, a conveying belt, and an attracting conveying unit that attracts an uppermost sheet to the conveying belt and conveys the same.
The air sheet feeding apparatus requires a time period from when driving of a fan is started to when sheets are ready to be fed, because air is blown. To reduce the time period required for sheet feeding in a case where sheets are fed selectively from a plurality of sheet feeding cassettes, the fan should be left driven, but in this case, the useful life of the fan is decreased due to increased power consumption. On the other hand, when driving of the fan is stopped after sheet feeding from one sheet feeding cassette completes, it takes time to feed a sheet from that sheet feeding cassette again, resulting in the productivity of the image forming apparatus decreasing.